Hydraulic steering mechanism for airplanes



Dec. 25, 1951 R LEVY HYDRAULIC STEERING MECHANISM FOR AIRPLANES Filed Oct. 28, 194'? Patented Dec. 25, 1951 HYDRAULIC STEERIN G MECHANISM FOR AIRPLAN ES Rcn Lucien Levy, Paris, France, assignor'toSociete dlnventions Aeronautiques et Mecaniques S.'I. A. M., Geneva, Switzerland, a corporation of Switzerland ApplicationOctober 28, 1947, Serial No. 782,617 r In. France November 5, 1942 The invention refers to steering mechanisms of vehicles and more particularly to hydraulic steering mechanisms of airplanes.

According to the main feature of thepresent invention, a steering member, such as a rudder, a steerable tail wheel or'the nose wheel of a tricycle landing gear is subjected to a hydraulic force tending constantly to bring it back in its median orneutralposition. Under such conditions,-the median orneutral position of the steering memberis a stable position, that is, this member remains in this position as long as the pilot does not operate the manual control provided for its displacement. Furthermore after it is displaced from this median or neutral position in either direction by the pilot toeifect a steering operatiomthe steering member tends to return automatically to neutral position as soon as the pilot frees the steering control member.

According to anotherfeature of the invention, the intensity of this hydraulic return forcemay be adjustedat will. ,Thus, ,forinstance, in the case of the tail wheel of an airplane, or of the nose wheel of atricycle-landing gear, it becomes possible to adjust the relative amount of freedom left to thiswheel with respect to its steering displacements and-thereby toensure the optimum behaviour of said wheel on the ground during taxiing operations.

According to a further feature of the invention,

this hydraulic return force -is advantageously side of its median or neutral position. This-condition must be taken into account in the case of application of the invention to tail wheels or nose wheels of tricycle landing gears of airplanes in order tofacilitate'the manoeuver oft-he aircraft on the airport andinthe hangars.

It'is also an object of the presentinvention to provide a steering mechanism capable of fulfilling this condition. Thus full-castering mechanism may be associated with any type ofsteering mechanism, independently of the provision of the above-mentioneddevice for the automatic mg gear for aircraft.

3C1aims. (Cl. 24450) return, of thesteering member. For instance, it may be applied to mechanically, pneumatically or electrically controlled steering mechanisms and/or automatic return devices ofitheabovementioned type.

Essentially, ina preferred form. of the present. invention, this latter consists in .connectingthe steering member throughthe intermediary-eta transmission device of the eccentric type allowing for its full or castering aboutits pivot on either side of its median or neutral position, Without interfering with the controlled steering and/or automatic return operations.

Obviously the presentinventionmaybe applied, not only to a compound system, of steering control and ofautor'natic ret'urn'bf' 'a steering member, hutalso toany systemlofsteeringcontrol or of automatic return of castering members and is not to be limited solely to application in the field of aeronautics.

Other objects, features and advantagesofthe present invention will appearin the following description, made in reference'to the accompanying drawings, in which:

The figure is .a diagrammatic view of ferred embodiment of the invention.

Referring to the drawing, thesteering member ,a prec which is to be controlled and returned ,to ,a

neutral position can constitutethe spindle of a steerable wheel such as embodied in the conventional tail wheels or the, nose wheels of land- The median or neutral position ,of this spindle is denoted at :n-- 1,/. An eccentric crankpin Zis carried hy'the steeringmember orspindle a and thispin is pivotally mounted in ,a block ,3 which in turn is :slidably mounted in the rectangular guide openingltoia frame or cage 5. As indicated; the oppositesides of the frame or cage are integral with .rods 12 and'ta respectively constituting the rods or shanks of operating pistons us and m. I'hesepistons are slidably mounted in symmetrically disposedcylinders v4 and v5 which respectively are on :opposite sides "of the line. defining the median or neutrol-positionof the spindle a. The pistons divide the cylinders 04 and Us into two chambers con stituting inner chambersadjacent the frame or cage 5 and outer chambers between the -outer faces of the'pistons ue and w: and the endwalls of the cylinders.

Outwardly of the cylinders :14 and vs are secondary cylinders its and lcvrespectively coaxiall'y aligned with the operating cylinders and provided with inturned annular shoulders 7'4 and is-at the inner ends thereof which partially close these secondary cylinders. Slidably mounted within these secondary cylinders are secondary pistons constituting automatic return pistons Z6 and 17 respectively embodying fingers or rods 14 and Z which in turn are in cooperative contact with the respective outer faces of the main or operating pistons us and 141- As is apparent, the annular shoulders 7'4 and is limit the stroke of pistons Z6 and Z7 toward the spindle a.

Inasmuch as the operating ,pistons tz and is are in alignment with the automatic return pistons Z6 and Z7 and the'operating pistons are through the eccentric pin 2 coupled with the spindle a the latter may be displaced through an arc of i180 through the median or neutral position my and on opposite sides thereof. This displacement of the spindle is responsive to the rectilinear displacement of the operating pistons us and 1L7 and also to the rectilinear displacement of the secondary or automatic return pistons l6 and Z7. 7

The operating and returning pressure is fluid pressure furnished by an oleo-pneumatic accumulator q of large capacity and suitable fluid circuits which include the conduits z, w and w, the latter connected respectively with cylinders U4 and v5 and conduits p, n, m and ml. the latter connected respectively with the cylinders ks and k7. The flow of fluid from the accumulator to and from the operating cylinders is controlled by a manually operable selector valve or distributor :c of a known type including an operating handle 1 This valve is connected with the conduits w and wi, the main conduit leading from the accumulator z and a return conduit si in such fashion that by suitable manipulation of the handle y in either direction fluid under pressure can flow from the accumulator through conduit wi into cylinder v5 and whereupon return fluid flows from 1 cylinder in through conduit w, distributor x and conduit .91, or upon reverse 'movement of the handle the fluid will flow into conduit w and cyl inder v4 and out of cylinder 05 through conduit an, the distributor and conduit .91. In the position ill-ustratedthe fluid from the accumulator q does not pass through the distributor and the v conduits w and m are in circuit with one another.

The fluid supply to the secondary cylinders includes the conduit p and an adjustable pressure reducer o mounted between conduits p and n. A tank s receives the return flow through the conduit .91 and a conduit s2 extends between the tank and the accumulator. In this latter conduit is interposed a pump s3 and between the pump and accumulator q is a check valve s4, the pump functioning to recharge and maintain the pressure in the accumulator.

As previously indicated, with the hand lever y in neutral position as shown the conduits w and an are connected and the spindle a occupies its median or neutral position x-y.

Upon any tendency of the spindle a to move out of its neutral position, for instance in the direction of the arrow ii, the torque generated by the spindle wouldtend to move the rod its and piston in to the right and through contact of the outer face of the piston in with the rod or finger 15 the piston Z7 would likewise have a tendency to move to the right. The fluid flows through conduit n and the pressure reducer 0 toward the accumulator q. However, the pressure existing in this accumulator opposes the return fluid flow and imparts a resilient return action to the pis. ton 11 to restore and maintain through contact 4 of the plunger or finger It with piston 1'11 the spindle a at its neutral position. At the same time the fluid expelled from cylinder '04 passes through conduit w, the distributor a: and conduit 1.01 into cylinder 05. The adjustable pressure reducer 0, however, can be so adjusted as to provide that the pistons Z6 and Z7 lock the spindle in the median or neutral position under normal disturbing torques so that the pistons us and uv are unable to move except and unless direct fluid pressure from the accumulator is exerted thereon.

Thus, in order to submit the spindle a to steering action so as to make the same turn in the direction of the arrow h the handle y is moved to place the fluid under pressure in conduit 2 in communication with the conduit wi and thence into operating cylinder '05 and simultaneously the conduit w is placed in communication through the distributor with conduits s1 and thus the tank. Under these circumstances the pistons m and us will respectively move to the right, thereby imparting a turning action to spindle a and the fluid expelled by piston Z7 from cylinder Zc-z returned through the pressure reducer 0 so that the steering action can be effected.

The pump s3 as indicated recharges the accumulator ,f.

When the handle 1/ resumes its neutral position following steering action to the right the pressure in the accumulator then permits recharging of cylinder k7 to restore the spindle a to its median position, the excess fluid from pressure chamber or in cylinder 2'25 flowing through conduits 101 and w into pressure chamber in; of cylinder in.

It is therefore clear that uponmovement of handle 1/ in the opposite direction pressure fluid flows into pressure chamber Us through conduit 10 to move piston us to the left with the fluid expelled from chamber ks passing through conduits m and n and the excess fluid from pressure cylinder '07 flowing through distributor s and conaccumulator pressure operating through conduits m and n and entering cylinder ks restores the spindle to its median or neutral position.

It is therefore clear that as applied to steering wheels for airplanes the present invention facilitates steering control, restores the steering wheel automatically back to its median or neutral position and renders it possible to lock this steering wheel during take-off and landing.

What is claimed is:

l. Hydraulic steering mechanism more particularly for aircraft landing gear comprising a ro tatable spindle movable through an arc of from opposite sides of a neutral position, an eccentric member on said spindle, a pair of primary hydraulic cylinders mounted in spaced relation to and on opposite sides of said spindlep,

an operating piston in each cylinder defining a variable volume pressure chamber therein, means mary cylinders, a secondary piston in each secondary cylinder, rods on each secondary piston movable within the respective primary cylinders and contacting the outer faces of the operating pistons therein, an oleo-pneumatic accumulator, a tank, a four-way distributor and conduit means connecting said distributor respectively with said accumulator and tank and to the pressure chambers of the operating cylinders, conduit means interconnecting said secondary cylinders, an adjustable pressure reducer in communication with said last mentioned conduit means, and conduit means connecting said pressure reducer in communication with said accumulator.

2. Hydraulic steering mechanism more particularly for aircraft landing gear comprising a rotatable spindle movable through an arc of i130 from opposite sides of a neutral position, a guiding frame, a block slidably mounted within said frame, an eccentric crank pin pivotally mounted in said block and carried by said spindle, a pair of operating pistons integral with said frame and extending from opposite sides thereof,

a pair of primary hydraulic cylinders mounted in spaced relation with respect to and on opposite sides of said spindle and receiving said pistons, said pistons defining variable volume pressure chambers within said cylinders, a pair of fingers each in cooperative contact with the outer face of one of said pistons and slidable through said cylinders, return pistons carrying said fin gers and a pair of secondary hydraulic cylinders receiving said return pistons, an oleo-pneumatic accumulator, a tank, a controllable four-way distributor, conduits connecting said distributor respectively to said accumulator and tank and to the pressure chambers in the respective primary cylinders; conduit means interconnecting said secondary hydraulic cylinders. an adjustable pressure reducer connected to said last mentioned conduit means and conduit means connecting the pressure reducer to the accumulator, said distributor in normal condition blocking flow from said accumulator to said pressure chambers so that fluid pressure from said accumulator through the pressure reducer and into said secondary cylinders maintains said spindle in a median position but upon controlling said distributor to permit fluid fiow selectively into either said pressure chambers rectilinear movement of said operating pistons imparts rotatable steering movement to said spindle.

3. Hydraulic steering mechanism as defined in and by claim 2 including conduit means providing a connection between said accumulator and said tank, a recharging pump connected to said conduit means and a check valve in said conduit means and between the pump and the accumulator.

RENE LUCIEN LEVY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,251,563 ODonnell Jan." 1, 1918 2,254,935 Darling Sept. 2, 1941 2,401,364 Mercier June 4, 1946 FOREIGN PATENTS Number Country Date 851,580 France Oct. 2, 1939 

